1. Field of Invention
The present invention relates to a developing device having an exchangeable toner box.
2. Description of Related Art
A conventional developing device used in a laser printer includes a toner hopper and a developing chamber. The toner hopper holds a non-magnetic, single-component toner or other type of toner. The developing chamber is provided with a developing roller, a supply roller, and a layer-thickness regulating blade.
The toner hopper holds only a finite amount of toner that needs to be replenished as toner is used up during developing operations. Toner boxes filled with new toner can be provided separately for replenishing the used up toner in the toner hopper. In one known configuration, the toner box is formed with a hole that is covered with a film. The toner box is mounted on top of the toner hopper so that the hole in the toner box is aligned with an opening formed in the upper portion of the toner hopper. After the toner box is mounted, the film is removed so that toner falls from the toner box into the toner hopper. However, this configuration has a problem in that the toner can leak out from the opening or the operator""s hands can become stained with toner because the opening in the toner hopper is exposed.
To overcome this problem, some developing devices are provided as an independent drum cartridge that can be attached to and detached from an image forming device. When all the toner in one drum cartridge is used up, then the entire drum cartridge is replaced with a new one. With this configuration, new toner can be provided for developing operations without fear of toner leaks or staining the operator""s hands. However, generally the developing device runs out of toner before the developing roller has reached the end of its useful life, that is, while the developing roller is still in a usable condition. When toner is replaced by replacing the entire drum cartridge, the developing roller is also replaced so the developing roller is wasted.
To overcome this problem, one type of developing device is made with just the toner hopper portion in the form of a cartridge, rather than the entire developing device. With this configuration, only the toner cartridge is replaced when the developing device runs out of toner. As a result, the developing roller in the developing chamber can be effectively used without fear of toner leaks or toner stains occurring during exchange of the toner cartridge.
However, this configuration also has room for improvement. Not all toner that is supplied from the toner hopper to the developing chamber is used during the image developing process. Some toner collects and accumulates in the developing chamber. This toner has degraded quality. For example, non-magnetic, single-component toner is easily degraded by stress applied during the developing process. The degraded toner can remain in the developing chamber even though the toner cartridge is replaced and can mix in with new toner from the new toner cartridge because of shocks that occur when the new toner cartridge is mounted onto the developing device or because of vibration applied to the developing device after the new toner cartridge is mounted. Problems can occur when the degraded toner mixes with new toner. For example, because toner is charged by a very sensitive mechanism, if a great deal of degraded toner remains in the developing chamber, then oppositely charged toner, that is, toner particles with a charge opposite of the normal particle charge, can be generated that results in fog, degradation of the image quality, and variation in image quality.
It is an objective of the present invention to overcome the above-described problems and provide a developing device, and an image forming device that uses the developing device, that prevent problems such as occurrence of fog, degradation of the image quality, and variation in image quality from occurring even after a toner cartridge is replaced.
To achieve the above-described objectives, a developing device according to the present invention includes an exchangeable developing-agent holding portion, a developing portion, and a developing-agent moving means. The developing-agent holding portion and the developing portion are freely detachably attached to each other. The developing-agent holding portion holds developing agent and has a through hole for supplying the developing agent. The developing portion is in fluid communication with the through hole of the developing-agent holding portion. The developing portion includes a developing-agent bearing body that has a surface bearing developing agent supplied from the developing-agent holding portion through the through hole. The developing-agent moving means functions to move residual developing agent from the developing portion into the developing-agent holding portion before the developing-agent holding portion is exchanged for a new developing-agent holding portion.
An image forming device according to the present invention includes a housing, a latent image bearing unit, a developing unit, and a developing-agent moving means. The developing unit is freely detachably attached to the housing and includes an exchangeable developing-agent holding portion and a developing portion. The developing-agent holding portion holds developing agent and has a through hole for supplying the developing agent. The developing portion is in fluid communication with the through hole of the developing-agent holding portion. The developing portion includes a developing-agent bearing body that has a surface that bears developing-agent supplied through the through hole of the developing-agent holding portion. The developing-agent bearing body transports developing agent borne on the surface to a latent image borne by a latent image bearing unit. The developing-agent holding portion is freely detachably attached to the developing portion. The developing-agent moving means functions to move residual developing agent from the developing portion into the developing-agent holding portion before the developing-agent holding portion is exchanged for a new developing-agent holding portion.